Hemiallen the 17.5cc dome is what thay list that is around 15:1 with a 72cc chamber there listing. along with only .090 valve to pistion clearance I end up with .039 pistion to head clerance. I have zinged it out past 7500 a fue times I had to put a 7800 chip in it as I was going into the 7600 chip. but the plugs have looked ok after so I guess it is got enough clerance. I dont normaly shift it past 6800 and trap 7200. but when I shift at 7200 it goes 7600.